1. Field of the Invention
This invention relates to wood preservative compositions and methods.
2. Description of the Prior Art
Wood requires treatment with microbicides to prevent staining and decay by microorganisms. By wood is meant lumber, timber, posts, wood coverings, wicker, millwork, joinery, wood products such as plywood, fiberboard, chipboard, waferboard, particleboard, and other wood products used in construction.
Freshly milled timber and wood for millwork/joinery are usually treated with preservatives by dipping and double vacuum treatments. Wood for use in ground and many above ground applications are usually treated with a preservative by pressure treatment. Preservatives can also be applied by brushing, spraying, soaking, and similar treatment methods.
The most important current commercial wood preservative, especially for pressure treating applications, is CCA (chromated copper arsenate). After treatment with CCA, there is a waiting period to allow for fixation of the metals into the wood before it can be used. During this fixation period, ground contamination from chromium, copper, and arsenic can occur if proper containment procedures are not followed. While CCA is very effective for wood preservation, disposal of unwanted CCA treated wood is becoming a problem. In some places, unwanted CCA treated wood is considered hazardous waste requiring special disposal procedures. There is also concern about leaching of copper, chromium and arsenic from CCA treated wood during its use.
As an alternative to CCA, certain water insoluble organic preservative compounds have been proposed. Such organic compounds do not require a fixation period and unwanted treated wood should not be considered hazardous waste. U.S. Pat. No. 4,954,338 teaches microemulsions of isothiazolone wood treatment compounds which require the use of certain surfactants. European Patent Application 0148526 discloses a water-dilutable formulation for the azole class of preservatives with preferred surfactants. Upon exposure to water, the organic wood preservative compounds applied by prior methods and compositions are all believed to suffer from the problem that the preservative leaches from the wood at too great of a rate.